The present invention relates generally to a shock absorber control apparatus for use in motor vehicles, for example, and more particularly to a damping force detector for detecting a damping force of a shock absorber to adequately control the shock absorber in accordance with the damping force detection result.
Preferably, motor vehicles are equipped with a variable damping force type shock absorber so as to take a countermeasure for rapid variation of the state of the vehicle running road, thereby stabilizing the motor vehicle to give a comfortable ride to passengers in the vehicle. The adequate control of the shock absorber is based upon quick and accurate detection of the damping force of the shock absorber.
Various types of shock absorber control apparatus have been devised heretofore. One known arrangement is disclosed in the Japanese Utility Model Provisional Publication No. 61-67009, the technique of which is made so as to detect the displacement of a variable damping force type shock absorber and change the damping force of the shock absorber in response to the variation speed of the displacement taking a predetermined value. Another approach, such as is disclosed in the Japanese Patent Provisional Publication No. 62-29410, involves controlling the detection sensitivity of a damping force indicating signal generated from a damping force sensor of a variable damping force type shock absorber, in accordance with the setting state of the damping force of the shock absorber and adequately determining the damping force of the shock absorber in accordance with the road surface states and the vehicle running conditions.
However, such prior art techniques cannot produce satisfactory results for meeting requirements in terms of adequately controlling the shock absorber so as to stabilize the motor vehicle to give a comfortable ride to passengers. That is, because the variation speed of the displacement and the damping force of the shock absorber are actually in non-linear relation to each other, difficulty is encountered to detect the damping force on the basis of the displacement variation speed. In addition, the displacement detecting means is made up of a detection coil acting as a so-called differential transformer which is arranged to detect the variation of inductance due to expansion and contraction of the shock absorber, and the detection coil provides problems in terms of durability and reliability. Even if using an optical sensor or an ultrasonic sensor in place of the detection coil, the optical sensor and the ultrasonic sensor respectively have the inherent problems. Besides, in the case of changing the detection sensitivity of the output signal of the damping force sensor in accordance with the setting state of the damping force, there is a problem that the circuit arrangment becomes complex. Further, in changing the detection sensitivity of the output signal of the damping force sensor, the changing timing is adequately determined, and the inadequate changing timing causes vibration of the motor vehicle.